“The Department of Defense takes seriously all credible reports of civilian deaths and injuries. We hold ourselves to high standards of conduct and accountability,” she said.

“In those instances in which civilians have been killed or injured, after-action reviews have been conducted to determine why, and to ensure that we are taking the most effective steps to minimise the risk of civilians being killed or injured in the future.”

Amnesty said the vast majority of family members it interviewed said they had never been interviewed by US military investigators.

“None of the cases that we looked into, involving more than 140 civilian deaths, were prosecuted by the US military,” Richard Bennett, Amnesty International’s Asia Pacific Director, said in a statement.

“Evidence of possible war crimes and unlawful killings has seemingly been ignored.”

‘War crimes’

In two of the cases, one in Paktia province in 2010 and another in Wardak province from November 2012 to February 2013 Amnesty’s report said there was “abundant and compelling evidence of war crimes”.

The Department of Defense said it “takes seriously its obligation to treat humanely all individuals in its custody, and it investigates all credible allegations of misconduct. We take vigilant action to prevent such conduct and to hold any such perpetrators accountable for their wrongful acts.”

A spokesman for NATO forces in Afghanistan, Lt. Col. Chris Belcher, said authorities were reviewing the report and would respond later.

Afghan civilians increasingly find themselves under fire as the 2001 US-led war draws to a close, as Afghan forces take the lead in operations targeting the Taliban.

A UN report earlier this year said 1,564 civilians were killed from January through June, compared with 1,342 in the first six months of 2013.

In its report, Amnesty International said US and NATO forces have made significant strides towards preventing civilian casualties, though lingering questions over the 10 incidents it cited casts a pall over their efforts.

“The legacy of international military operations is seriously tainted, however, when military forces leave behind families whose efforts to seek justice have been ignored,” the report said.